In general, bumper systems for a vehicle are required to satisfy low speed crash tests and property insurance regulatory agency (RCAR, IIHS) tests, which are regulations. In this case, the required performance of the property insurance companies, which have a great influence on automobile sales, is more demanding than the regulations. For example, in the RCAR test, after two tests, i.e., a 40% and 10 degree offset barrier test and a bumper dummy barrier test are performed, the repair costs are calculated with respect to the damage of the vehicle body, and performance of one or both of the two tests is requested regionally.
Thus, a bumper beam and a crash box, which constitute the bumper system for the vehicle, should have a structure in which crash energy is maximally absorbed by compression/deformation/destruction in the 40% and 10 degree offset barrier test of the RCAR test, which is required by the property insurance companies. Since the performance required by the property insurance companies is high, most manufactures have applied high-strength composite plastic materials and high-strength steel materials to the bumper system. However, when the materials are applied, the costs increase in proportion to the increase in strength. Also, since the regulatory performance required in each area and the performance required by the property insurance companies are different from each other, the bumper system to be developed has to increase in specification.
For example, as illustrated in FIG. 1, the European bumper system (see FIG. 1A), the North America bumper system (see FIG. 1B), and the domestic bumper system (see FIG. 1C) are different in specification of the bumper beam and the crash box according to sales areas.
Thus, a crash box for a vehicle, which is capable of absorbing energy while the crash box is sequentially crashed down on an shock, is disclosed in Korean Patent Registration No. 10-1327016 (hereinafter, referred to as a “prior art 1”). However, the prior art 1 does not specifically disclose a method for fastening the crash box to a vehicle body, although a member is minimized in damage by matching cross sections of the crash box and the member. Thus, according to the prior art 1, there is a problem that accessory parts have to be added for fastening the vehicle body, resulting in making it practically difficult to reduce a weight. Also, the crash box has to be crashed down from an impacted portion, i.e., a front portion in order to prevent the vehicle body from being damaged. In case of the prior art 1, it is difficult to easily induce the abovementioned feature, and also, it is difficult to commercialize the abovementioned feature because it does not take into consideration of an escaping hole of a bolt for towing.
A crash box for a vehicle, in which a steel crash box is optimized in shape in a general bumper beam module system, is disclosed in Korean Patent Registration No. 10-1358294 (hereinafter, referred to as a “prior art 2”). However, in the prior art 2, although a structure in which the crash box is sequentially pressed from a front portion that is a crash site is provided, when considering the bumper barrier test that is added recently, there is a limitation in applying of the prior art 2 as it is. Also, even if applied, it is expected to increase in weight due to an increase in strength of the bumper beam.